Traditional fuel metering systems for gas turbine engines embody a metering valve, a head regulator to maintain a constant differential pressure across the metering valve and a shut-off valve. In order to achieve a minimal cost, the aforementioned components generally operate at low force levels. Operation at low force levels has the drawback of fostering hysteresis owing to contaminants becoming interposed between moving parts and close fits between the parts themselves.
The utilization of high frequency, time modulated ball valves for metering fuel is known in the prior art. Certain fuel metering systems in automobiles employ pulsed solenoids in order to interrupt the flow to the engine in such a manner as to produce a desired flow rate. However, flow stoppages of this nature engender pressure spike fluctuations which affect the proper functioning of upstream elements. In addition, a known gas turbine engine fuel control utilizes a pulsed solenoid to apportion a constant flow of fuel between the engine burner nozzles and a bypass loop. Such a latter mentioned fuel control is described in U.S. patent application Ser. No. 183,059, entitled Fuel Control Method and Apparatus and filed on Sept. 2, 1980 in the names of Robert E. Peck and Raymond D. Zagranski.